Page:Proceedings of the Royal Society of London Vol 1.djvu/391

Rh of other quadrupeds, and in greater or less degree according to the different qualities of their food, it was natural to expect some correspondent peculiarities in the gizzards of those birds which feed on grass, to ﬁt them for digesting this kind of food.

With this view the author has examined the gizzards of the goose and swan, in comparison with that of the turkey, which feeds on a different kind of food.

For the purpose of rendering the ﬁbres distinct, so as easily to be traced, the gizzards of each were boiled, after having been previously ﬁlled with plaster of Paris. In the turkey the two muscles, of which the gizzard consists, are of unequal strength, that on the left side being considerably stronger than that on the right. These muscles, by their alternate action, produce a constant friction on the contents ; for though the direct pressure inwards is very great, the lateral mo- tion occasions the force employed upon the substances contained, to be applied in an oblique direction, as Spallanzani and others have observed.

The internal cavity being of an oval form, like a pullet's egg, rounded on all sides, does not allow the opposite sides ever to come into contact; so that the food is triturated merely by the intermixture of bodies harder than itself.

In the goose and swan, on the contrary, the cavity is ﬂattened, with its edges very thin. The surfaces applied to each other are, however, not plane surfaces; but a concave surface is applied to one that is convex; and in the left side the concavity is above; but the curvature changes, so that on the right side the concavity is below. In these gizzards the horny covering of their surface is much stronger than in the turkey, and rough; so that by a sliding motion of the parts opposed, the food is ground, although they do not admit the intervention of hard substances of a large size, and almost without requiring such assistance.

In the lower palt of the oesophagus of these birds, the author ob- serves an enlargement, which he considers peculiar to them, and thinks it answers the purpose of a reservoir, in which the grass is re- tained, macerated, and prepared, as in ruminating animals, for the subsequent process of rumination.

Mr. Groombridge being in possession of a transit circle four feet in diameter, made by Troughton, undertook a series of observations upon circumpolar stars, for the purpose of determining the latitude of his observatory.